What is national grid?

What is the difference between isolated grid and central grid?

• If I install photovoltaics on a building for example, is it isolated or central grid? I'm not quite sure what these term meant. Is it about the energy storage system (isolated is storing the energy locally while central is connect to the grid and links to the mains?)

• Answer:

  The isolated grid means a closed loop system like you might find on a farm where a solar cell charges batteries and inverters and items are powered solely by the solar cells. A central grid is what the case usually is, where you are providing solar power to a pre-existing grid (like a home or office building). Anything plugged into a wall outlet could draw power either from the solar cells or from the existing power grid.